1. Field of the Invention
The present invention relates to a disc brake for a vehicle. More particularly, the invention relates to a structure of the disc brake which is capable of preventing an abnormal sound from being generated, when the disc brake is operated, at an engaging portion where a pad and a support portion, which are assembled into the disc brake, engage with each other.
2. Description of the Related Art
A disc brake having a structure as shown in FIGS. 6 and 7 is known as a disc brake for a vehicle. The disc brake is disclosed in JP-A-9-79296. As shown, a support member 2 is disposed close to a part of a rotor 1, which rotates together with a wheel (not shown) of the vehicle. The support member 2 is firmly supported on a suspension device (not shown) provided on the vehicle body side. The support member 2 supports a caliper 3 in a state that the caliper 3 is movable in the axial directions of the rotor 1 (the axial direction is back-and-forth direction, in other words, direction vertical to the drawing surface of FIG. 6, or is vertical direction when viewed in FIG. 7). A pair of run-in and run-out side support portions 4 and 5 are located at both ends of the support member 2, while being spaced apart from each other in the circumferential direction of the rotor 1. The top ends of those support portions 4 and 5 are each bent to be shaped like U. Each of the support portions 4 and 5 is disposed astride the outer peripheral portion of the rotor 1 in the vertical direction in FIG. 6 (in other words, vertical direction when viewed in FIG. 7). The first ends of pads 6 are supported by the run-in side support portion 4, while being slidable in the axial direction of the rotor 1. The second ends of those pads 6 are supported by the run-out side support portion 5, while being also slidable in the axial direction. The run-out side support portion 5 receives brake torque, which is generated, when the braking is effected, by friction of the pads 6 against the side surfaces of the rotor 1 and act on those pads 6. In the embodiment, the run-out side support portion 5 is located at the run-out side end (in other words, left end in FIGS. 6 and 7 when the rotor 1 is rotated from the right side to the left side, in the direction "a" of an arrow in FIGS. 6 and 7).
Engaging protrusions 8 are protruded from both ends of a back plate 7 of each pad 6. Engaging grooves 9 are formed in the inner side surfaces of the run-in side and run-out side support portions 4 and 5, respectively. The engaging protrusions 8 are respectively brought into contact with the engaging grooves 9 such that the engaging protrusions 8 are movable in the axial direction of the rotor 1, and the engaging portions will be referred to as a run-in engaging portion and a run-out engaging portion. Thus, the pads 6 are respectively movable to and from the side surfaces of the rotor 1, while being supported on the support member 2.
The caliper 3 is supported by the support member 2 while straddling the pair of the pads 6. The caliper 3 is provided with cylinder portions 10 and caliper claws 11. The cylinder portions 10 include pistons for pressing the pads 6 against the rotor 1.
Pad clips 12, which is formed with an elastic metal plate, for example, a stainless steel plate, are provided at the portions of the support member 2 where the support member supports both ends of the pads 6. The pad clips 12 elastically press the pads 6 to thereby prevent unsteady motions of those pads, which is caused by rattling during the vehicle running. Each of the pad clips 12 partly covers the inner surface of the corresponding engaging groove 9. In this case, a small clearances 13 exist between the part of the pad clip 12 where the pad clip covers the inner surface of the engaging groove 9 and the corresponding engaging protrusion 8. The clearances 13 are dimensionally selected so as to secure smooth displacement of the pads 6 in the axial direction of the rotor 1 in a normal state, and further even when the back plates 7 and/or the support member 2 are varied in dimension. The back plates 7 are formed with stainless steel plates and the support member 2 is made of cast iron. Accordingly, those component parts become rusty. In this case, the resultant products somewhat vary the dimensions of those and related component parts. For example, the corrosive products formed on the back plates 7 yield slight dimension increase of the back plates 7 or the outside dimensions of the engaging grooves 9 are also somewhat varied.
In the conventional disc brakes having the structure shown in FIGS. 6 and 7, the clearances 13 are selected to be wide enough to allow the pads 6 to smoothly displace in the axial directions of the rotor 1 even when the outer periphery edge of the back plates 7 and/or the support member 2 made of cast iron are rusted, and as a result, the back plates 7 increase their dimensions and the engaging grooves 9 decrease their dimensions. With use of such clearances 13, the pads 6 sometimes rapidly moves with respect to the support member 2. When the disc brake is operated for braking the vehicle, the pads 6 come into frictional engagement with the rotor 1, and are displaced in the circumferential direction of the rotor 1. At this time, the clearances 13 associated with the run-out side support portion 5 disappear, while at the same time the back plates 7 impact against part of the pad clips 11, to thereby generate a beat sound, called a cronk sound. Also when the disc brake is not operated, the pads 6 displace while resisting the elastic force by the pad clips 12, to sometimes generate noisy vibrations called rattle sounds. Increasing the elastic forces of the pad clips 12 may prevent generation of such noisy vibrations. However, this approach is not desirable for the following reasons. The elastic force increase makes the assembling work of the disc brake complicated, and further restricts movements of the pads 6, and hence a drag resistance increases between the pads 6 and the rotor 1 in a non-braking mode.